For example, in a mobile telephone terminal, often a whip antenna that can be expanded and contracted (or that can be placed in and taken out of a housing) is installed and a wireless circuit, etc., is built in a housing that can be deformed. The housing or metal such as a shield case in the housing may be used as an antenna or an antenna component.
In a mobile telephone terminal installing a whip antenna that can be expanded and contracted, generally a communication function can be used in any of two modes of a storage state in which the antenna is contracted and an expansion state in which the antenna is taken out to the outside and is expanded.
Often, a housing of a mobile telephone terminal is separated into an upper housing and a lower housing, which are connected through a hinge, whereby deformation operation of opening/closing or rotation is possible. Further, in a mobile telephone terminal using a housing, etc., as an antenna, often a communication function using the antenna containing the housing can be used in any of two modes of a state in which the housing is folded to a small size and a state in which the housing is opened to an elongated state.
However, for example, to use the whip antenna that can be expanded and contracted in an expansion state and a storage state, change in the impedance characteristic is not avoided. Likewise, to use the housing, etc., as an antenna, to use in a state in which the housing is closed and to use in a state in which the housing is opened, change in the impedance characteristic of the antenna is not avoided.
When the impedance characteristic of the antenna changes, it becomes impossible to correctly match impedance in a matching circuit placed between the antenna and a wireless circuit and a reflection wave increases in a signal transmission path and the communication characteristic of reception sensitivity, etc., is degraded.
Then, in a conventional mobile telephone terminal, for example, a small helical antenna may be adopted so that the impedance characteristic in the storage state of the antenna does not change as compared with the expansion state.
For example, Patent Document 1 discloses an art wherein matching is switched in response to used frequency band or communication mode in a portable wireless device. Specifically, it discloses an art wherein a parallel resonance circuit is turned on by a switch if necessary and an antenna is put into 2 resonance.
Patent Document 2 discloses an art wherein in an OFDM modulation signal receiver, a plurality of antennas are provided, separate amplifiers are connected to the antennas, signals from the antennas are diversity-combined using a weighting factor calculated based on carrier power to noise power ratio C/N (Carrier to Noise ratio) detected for each antenna channel.    Patent Document 1: Japanese Patent Laid-Open No. 2003-309489    Patent Document 2: Japanese Patent Laid-Open No. 2005-175878